1. Field of the Invention
This invention relates to a fuel injection timing control system for an internal combustion engine, more particularly to a fuel injection timing control system for a direct injection spark ignition engine, in which gasoline fuel is directly injected into the combustion chamber of the engine.
2. Description of the Related Art
A direct injection spark ignition engine has recently been proposed in which gasoline fuel is directly injected into the combustion chamber such that an ultra-lean burn combustion or a stratified combustion (in an ultra lean air/fuel ratio) or the pre-mixture charged combustion (in a uniform air/fuel ratio) occurs in the engine as is disclosed in, for example, Japanese Patent Publication No. Hei 4 (1992)-37264.
In the direct injection spark ignition engine, gasoline fuel injected at a timing or point insufficient for the gasoline fuel to vaporize may sometimes produce smoke. However, if fuel injection is merely exhibited in areas where smoke may occur, the engine torque will drop. This sometimes makes it difficult to achieve the desired engine torque. Here, xe2x80x9csmokexe2x80x9d indicates black soot made from unburned HC caused by oxygen poverty.
An object of the present invention is therefore to provide a fuel injection timing control system for an internal combustion engine, more particularly for a direct injection spark ignition engine which can ensure the engine torque drop is kept to a minimum extent, while avoiding smoke to occur.
This invention achieves this object by providing a system for controlling a fuel injection timing for a direct injection spark ignition internal combustion engine which is operated at an ultra-lean burn combustion or at a pre-mixture charged combustion, comprising; engine operating condition detecting means for detecting operating conditions of the engine at least including an engine speed and an engine load; fuel injection amount determining means for determining a fuel injection amount based at least on the detected engine speed and the engine load of the engine operating conditions; desired fuel injection start timing determining means for determining a desired fuel injection start timing at which injection of the determined fuel injection amount should be started based at least on the detected engine speed and the engine load; fuel injection start timing limit determining means for determining a fuel injection start timing limit by which injection of the determined fuel injection amount should be started based at least on the detected engine speed in accordance with predetermined data so as to avoid smoke from occurring in the engine; fuel injection timing comparing means for comparing the desired fuel injection start timing with the fuel injection start timing limit; fuel injection start timing correcting means for correcting at least one of the desired fuel injection start timing and the fuel injection amount, when the desired fuel injection start timing is found to exceed the fuel injection start timing limit in an advanced direction in crank angle, such that the fuel injection is started by the fuel injection timing limit. and fuel injecting means for injecting the determined fuel injection amount based on the determined fuel injection start timing.